Procurement and Analysis of Structural Fatigue Data

The most common type of structural fatigue test program is the experimental construction of an S-N curve and may be divided into two phases: determination of the mean fatigue limit by the staircase method; and determination of the finite life region and its subsequent analysis by regression analysis. The bases for statistical design of experiments require both randomization and, generally, replication. Randomization in sampling of material, specimen assignment to stress levels, and test sequence minimizes the effects of possible bias due to uncontrolled variation in material, laboratory environment, and test procedures. Replication of tests at a given stress level to estimate variability in fatigue life is often impractical. The variability in life may be estimated from regression analysis and used to predict probability of survival at any stress level.